Light

Cameras

How is a camera similar to, and different from, the eye?

A camera performs many of the functions of the eye. It has a lens to form an image on a photosensitive surface. The lens must be able to form sharp images of objects both close and far away. The amount of light reaching the photo detector must be controlled to make the exposure correct. In older cameras the photosensitive surface was film. Today cameras use a digital sensor. These sensors are small—most are between 3/8” and 1” in size—but contain as many as 10 million separate light detectors called pixels. Each pixel is covered by a red, green, or blue color filter so the camera can produce full-color images.

A camera’s lens isn’t flexible like the one in the eye, but the distance between the lens and the sensor can be varied. Bringing a distant object into focus requires that the lens be closer to the sensor. A close object requires that the lens be moved further away. The amount of light is controlled two ways. One is to have an aperture that can be opened to admit more light or closed down to reduce the amount of light. The second is a shutter that controls the amount of time light is allowed to reach the sensor. While leaving the sensor exposed for a longer amount of time is needed when the light is dim, it also will cause a blurred image if the object is moving. Thus it is important to select the correct combination of aperture and shutter speed to take good pictures.